Method of making a fuel cell device

ABSTRACT

A fuel cell device is prepared by dispensing and drying electrode and ceramic pastes around two pluralities of removable physical structures to form electrode layers having constant width and a shape that conforms lengthwise to a curvature of the physical structures. An electrolyte ceramic layer is positioned between electrode layers, forming an active cell portion where anode is in opposing relation to cathode with electrolyte therebetween, and passive cell portions where ceramic is adjacent the active cell portion. The layers are laminated, the physical structures pulled out, and the lamination sintered to form an active cell with active passages in anodes and cathodes and passive support structure with passive passages in ceramic. End portions of at least one of the two pluralities of physical structures are curved away from the same end portion of the other of the two pluralities resulting in a split end in the fuel cell device.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Pat. No. 10,355,300 issuedJul. 16, 2019 and entitled METHOD OF MAKING A FUEL CELL DEVICE, which isa continuation of U.S. Pat. No. 9,716,286 issued Jul. 25, 2017 andentitled METHOD OF MAKING A FUEL CELL DEVICE, which is a continuation ofU.S. Pat. No. 9,577,281 issued Feb. 21, 2017 and entitled METHOD OFMAKING A FUEL CELL DEVICE, which is a continuation of U.S. Pat. No.9,437,894 issued Sep. 6, 2016 also entitled METHOD OF MAKING A FUEL CELLDEVICE, which is a continuation of U.S. Pat. No. 9,023,555 issued May 5,2015, also entitled METHOD OF MAKING A FUEL CELL DEVICE, which claimsthe benefit of and priority to Provisional Application Ser. No.61/632,814 filed Feb. 24, 2012, the disclosures of which areincorporated herein in their entirety.

FIELD OF THE INVENTION

This invention relates to fuel cell devices and systems, and methods ofmanufacturing the devices and, more particularly, to a solid oxide fuelcell device.

BACKGROUND OF THE INVENTION

Ceramic tubes have found a use in the manufacture of Solid Oxide FuelCells (SOFCs). There are several types of fuel cells, each offering adifferent mechanism of converting fuel and air to produce electricitywithout combustion. In SOFCs, the barrier layer (the “electrolyte”)between the fuel and the air is a ceramic layer, which allows oxygenatoms to migrate through the layer to complete a chemical reaction.Because ceramic is a poor conductor of oxygen atoms at room temperature,the fuel cell is operated at 700° C. to 1000° C., and the ceramic layeris made as thin as possible.

Early tubular SOFCs were produced by the Westinghouse Corporation usinglong, fairly large diameter, extruded tubes of zirconia ceramic. Typicaltube lengths were several feet long, with tube diameters ranging from ¼inch to ½ inch. A complete structure for a fuel cell typically containedroughly ten tubes. Over time, researchers and industry groups settled ona formula for the zirconia ceramic which contains 8 mol % Y₂O₃. Thismaterial is made by, among others, Tosoh of Japan as product TZ-8Y.

Another method of making SOFCs makes use of flat plates of zirconia,stacked together with other anodes and cathodes, to achieve the fuelcell structure. Compared to the tall, narrow devices envisioned byWestinghouse, these flat plate structures can be cube shaped, 6 to 8inches on an edge, with a clamping mechanism to hold the entire stacktogether.

A still newer method envisions using larger quantities of small diametertubes having very thin walls. The use of thin walled ceramic isimportant in SOFCs because the transfer rate of oxygen ions is limitedby distance and temperature. If a thinner layer of zirconia is used, thefinal device can be operated at a lower temperature while maintainingthe same efficiency. Literature describes the need to make ceramic tubesat 150 μm or less wall thickness.

An SOFC tube is useful as a gas container only. To work it must be usedinside a larger air container. This is bulky. A key challenge of usingtubes is that you must apply both heat and air to the outside of thetube; air to provide the O₂ for the reaction, and heat to accelerate thereaction. Usually, the heat would be applied by burning fuel, so insteadof applying air with 20% O₂ (typical), the air is actually partiallyreduced (partially burned to provide the heat) and this lowers thedriving potential of the cell.

An SOFC tube is also limited in its scalability. To achieve greater kVoutput, more tubes must be added. Each tube is a single electrolytelayer, such that increases are bulky. The solid electrolyte tubetechnology is further limited in terms of achievable electrolytethinness. A thinner electrolyte is more efficient. Electrolyte thicknessof 2 μm or even 1 μm would be optimal for high power, but is verydifficult to achieve in solid electrolyte tubes. It is noted that asingle fuel cell area produces about 0.5 to 1 volt (this is inherent dueto the driving force of the chemical reaction, in the same way that abattery gives off 1.2 volts), but the current, and therefore the power,depend on several factors. Higher current will result from factors thatmake more oxygen ions migrate across the electrolyte in a given time.These factors are higher temperature, thinner electrolyte, and largerarea.

Fuel utilization is a component of the overall efficiency of the fuelcell. Fuel utilization is a term that can describe the percent of fuelthat is converted into electricity. For example, a fuel cell may onlyconvert 50% of its fuel into electricity, with the other 50% exiting thecell un-used. Ideally, the fuel utilization of a fuel cell would be100%, so that no fuel is wasted. Practically, however, total efficiencywould be less than 100%, even if fuel utilization was 100%, because ofvarious other inefficiencies and system losses. Additionally, if the gasmolecules can't get into and out of the anode and cathode, then the fuelcell will not achieve its maximum power. A lack of fuel or oxygen at theanodes or cathodes essentially means that the fuel cell is starved forchemical energy. If the anode and/or cathode are starved for chemicals,less power will be generated per unit area (cm²). This lower power perunit area gives lower total system power.

In a tubular fuel cell device, such as that shown in FIG. 1 where theanode lines the inside of the tube and the cathode forms the outersurface with the electrolyte therebetween, it is wishful thinking toexpect high utilization of fuel. The inside diameter of the tube, whichforms the fuel passage, is very large when compared to the thickness ofthe anode. Anode thicknesses may be on the order of 50-500 nm, whereastube diameters may be on the order of 4-20 mm. Thus, there is a highlikelihood of fuel molecules passing through the large fuel passagewithout ever entering the pores of the anode. An alternate geometry forthe tube is to have the anode on the outside of the tube. In that case,the problem could be worse because the fuel is contained within thefurnace volume, which is even larger than the volume within the tube.

Within a multilayer fuel cell device, such as the Fuel Cell Stick™devices 10 depicted in FIGS. 2 and 3 and developed by the presentinventors, fuel utilization can be higher because the flow path for thegas can be smaller. FIG. 2 is identical to FIG.1 of U.S. Pat. No.7,838,137, the description of which is incorporated by reference herein.Device 10 includes a fuel inlet 12 feeding a fuel passage 14 to a fueloutlet 16, and an oxidizer inlet 18 feeding an oxidizer passage 20 to anoxidizer outlet 22. An anode 24 is adjacent the fuel passage 14 and acathode 26 is adjacent the oxidizer passage 20, with an electrolyte 28therebetween. By way of example, both the anodes 24 and fuel passages 14can be made to a thickness of 50 nm, and this similarity in thickness,where the ratio of thickness can be near 1:1 (or a bit higher or lower,such as 2:1 or 1:2) can give a more optimal chance of molecule flow intoand out of pores.

These multilayer fuel devices 10 are built from green materials, layerby layer, and then laminated and co-fired (sintered) to form a singlemonolithic device having a ceramic support structure 29 surrounding oneor more active cells 50, each active cell 50 having an associated anode24, cathode 26 and electrolyte 28 fed by fuel and air passages 14, 20.An active cell 50 (or active layer 50) is one in which an anode 24 is inopposing relation to a cathode 26 with an electrolyte 28 therebetween,and the active passages are those that run along or within the activecell 50. FIG. 3 depicts two active cells 50. Areas of the device 10 thatlack an opposed anode 24 and cathode 26 are non-active or passiveportions of the device 10 that form the support structure 29, andpassive gas passages are those that run through these passive portionsof the device 10. The active cells 50 are “within” the device 10 andsubstantially surrounded by and supported by ceramic support structure29. The device has an exterior surface and internal supportingstructure, which is the ceramic support structure 29, such that theactive cells 50 are contained substantially inward of the exteriorsurface and are contained by the internal ceramic support structure. Itshould be understood that extension of all or a portion of an electrodeto an edge of the device for electrical connection at the exteriorsurface does not compromise the support of this structure as the activecell 50 is still within the interior structure, and is within the scopeof “substantially surrounded.” The electrolyte 28 in the active cell 50is monolithic with the ceramic support structure 29 by virtue of beingco-fired therewith, and may be made of the same or different material.In exemplary embodiments, the electrolyte 28 and ceramic supportstructure 29 are the same or similar in composition, with the primarydifference between them being that the electrolyte 28 is that portion ofthe ceramic material that lies between an opposing anode 24 and cathode26 (i.e., the middle layer in the 3-layer active cell 50) and theceramic support structure 29 is the remaining portion of the ceramicmaterial (i.e., the ceramic that surrounds the 3-layer active cell 50).Air and fuel are fed into the device 10 through the passive passagesthat are fluidicly coupled to the active passages that feed the activecells 50. Thus, a fuel passage 14 and an oxidizer passage 20, asreferred to herein, include both the passive and active portions of thepassages.

As discussed above, it is desirable to make the electrolyte 28 as thinas possible. However, as the electrolyte 28 is made thinner, the supportof the structure can be compromised, and distortion of the activeportion of fuel and air passages 14, 20 that feed the anodes 24 andcathodes 26 can occur at one or more locations within the active cell50, as well as distortion of the passive portions of the passages 14,20. These distortions in the passages 14, 20 may lead to leaks thatdegrade the performance of the affected active cell 50 and of theoverall device 10.

One advantage of the multilayer fuel cell devices developed by thepresent inventors is that many active cells 50 can be provided within asingle monolithic device, including multiple cells along a single activelayer and stacks of active layers one upon another, which can beconnected in various parallel and series arrangements, leading to asingle device with high output. If one area of one cell distorts, thereare still many other cells that produce power, such that the multilayerfuel cell devices are still superior to single cell tubular devices orstacked devices that are not monolithic. However, the more layers thatare incorporated, the higher the chance for multiple distortionsthroughout the device.

Therefore, there is a need to provide thin electrolyte layers whilestill providing the needed support to prevent distortion of the gaspassages within a monolithic multilayer fuel cell device.

SUMMARY OF THE INVENTION

According to an embodiment, a method of making a monolithic fuel celldevice is provided. A first paste of anode material and a second pasteof cathode material are dispensed around a first and second plurality ofspaced-apart removable physical structures, respectively, to at leastpartially surround each of the first and second plurality ofspaced-apart removable physical structures with the respective anode orcathode material, and a third paste of ceramic material is dispensedaround the first and second plurality of spaced-apart removable physicalstructures adjacent to the anode and cathode materials to at leastpartially surround each of the first and second plurality ofspaced-apart removable physical structures with the ceramic material.The first, second and third pastes are dried to form an anode layer anda cathode layer, each having a constant width and a shape that conformsin a lengthwise direction to a curvature of the first and secondplurality of spaced-apart removable physical structures, respectively.An intervening layer of ceramic material configured to function as anelectrolyte is positioned in a multi-layer stack between the cathodelayer and the anode layer, wherein an active cell portion of themulti-layer stack is formed by the anode material of the anode layer inopposing relation to the cathode material of the cathode layer with theintervening layer of ceramic material therebetween, and passive cellportions are formed by the ceramic material adjacent to the active cellportion in each of the anode layer, cathode layer and intervening layer.The multi-layer stack is then laminated and the first and secondplurality of removable physical structures are pulled out of thelaminated multi-layer stack to reveal spaced-apart active passagesformed through the active cell portion of each of the anode layer andthe cathode layer and spaced apart passive passages formed through thepassive cell portion of each of the anode layer and the cathode layer.The laminated multi-layer stack is sintered to form an active cellcomprising the spaced apart active passages embedded in and supported bythe sintered anode material and sintered cathode material and a passivesupport structure comprising the spaced apart passive passages embeddedin and supported by the sintered ceramic material and that transitionintegrally to the active passages within the active cell. At least oneend portion of at least one of the first and second plurality ofspaced-apart removable physical structures is curved in a direction awayfrom the same end portion of the other one of the first and secondplurality of spaced-apart removable physical structures resulting in asplit end in the fuel cell device to which separate gas inputs can becoupled.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the invention.

FIG. 1 is a schematic view of a tubular solid oxide fuel cell device ofthe prior art.

FIG. 2 is a schematic side cross-sectional view of a solid oxide FuelCell Stick™ device of the prior art.

FIG. 3 is a schematic end cross-sectional view of a solid oxide FuelCell Stick™ device of the prior art.

FIG. 4 is a perspective view of an anode layer formed by an embodimentof a method of the invention.

FIG. 5 is a schematic end cross-sectional view of a device formedaccording to an embodiment of a method of the invention.

FIGS. 6-9 are schematic cross-sectional views of anode layers formed byembodiments of a method of the invention.

FIG. 10 is a top view of an anode layer formed by an embodiment of amethod of the invention.

FIG. 11A is a partial cut-away top cross-sectional view of a deviceformed by an embodiment of a method of the invention.

FIG. 11B is a sequence of schematic partial cut-away top cross-sectionalviews depicting assembly of an anode layer formed by an embodiment of amethod of the invention.

FIG. 12A is a schematic top cross-sectional view of an anode layerformed by an embodiment of a method of the invention.

FIG. 12B is a schematic side view of a device formed according to anembodiment of a method of the invention.

FIGS. 13 and 14 are schematic top views of devices formed by embodimentsof a method of the invention.

FIG. 15 is a schematic end cross-sectional view of a device formedaccording to an embodiment of a method of the invention.

FIG. 16 is a sequence of schematic end cross-sectional views depictingassembly of an interconnect layer used in a device formed by anembodiment of a method of the invention.

FIG. 17 is a schematic top view of an anode layer formed by anembodiment of a method of the invention.

FIG. 18 is a schematic side cross-sectional view of a device formedaccording to an embodiment of a method of the invention.

FIG. 19 is a series of schematic top views and a schematic sidecross-sectional view depicting assembly of a series connection in adevice formed by an embodiment of a method of the invention.

FIGS. 20A and 20B are paired top and schematic side cross-sectionalviews depicting alternative anode interconnect tabs in the embodiment ofFIG. 19.

FIGS. 21A and 21B are a schematic side cross-sectional view and aschematic partial cut-away top cross-sectional view, respectively, of aseries connection in a device formed by an embodiment of a method of theinvention.

DETAILED DESCRIPTION

Reference may be made to the following patents and publications by thesame inventors, which describe various embodiments of a multilayer FuelCell Stick™ device 10 (et al.), the contents of which are incorporatedherein by reference: U.S. Pat. Nos. 8,278,013, 8,227,128, 8,343,684, and8,293,415, and U.S. Patent Application Publication Nos. 2010/0104910 and2011/0117471. The inventive structures and/or concepts disclosed hereinmay be applied to one or more of the embodiments disclosed in theabove-referenced published applications.

Various material terms will be used interchangeably, regardless of thestage of the material during manufacturing. For example, anode 24, anodelayer 24, anode material 24, etc. all refer to the anode itself or thelayer in which one or more anodes are positioned, irrespective ofwhether the anode material is in the form of a paste, a preform layer, asintered layer, an initial green state, or a final fired state.

In accordance with the present invention, to form the passive and activepassages in multilayer fuel cell devices, removable physical structures,such as wires, are placed in the anode and cathode layers of the deviceas the layers are assembled in the green state. The removable physicalstructures travel from one end of the device, through the active area,and are spaced apart from one another with the anode or cathode materialtherebetween. Previous designs used removable physical structure at theends of the device to form the passive passages, which were coupled tolarger areas of organic sacrificial material that were used inside thedevice to form the active passages. The wires were simply placed betweenpreformed sheets of green ceramic material with one end in contact withthe sheet of sacrificial material and the other end extending outsidethe end of the device. After lamination, during which the preformedsheets conform to the shape of the physical structures, the removablephysical structures were pulled out, and then the device was co-fired,allowing the sacrificial material to burn out and exit the end of thedevice through the passive passages and/or through other temporarybake-out ports in the sides. Despite embodiments that use ceramic ballsin the active area to help support the active passages, the large flatactive passages, as shown in FIG. 3, are still only partially supportedat best and sometimes distort as the sacrificial material bakes out. Asexplained above, distortions have occasionally led to leaks, which havedegraded the performance of the cell.

In the present method, the active area is assembled with removablephysical structures, such as fine wires, for example, 0.01 inch (0.254mm), that are spaced apart and surrounded by solid material. In otherwords, the removable physical structures are at least partiallysurrounded by solid material so as to embed them within a layer of greenmaterial, rather than placed between preformed layers. The removablephysical structures will be referred to as wires, interchangeably forease of discussion, with the understanding that the invention is notlimited to wires as the only possible removable physical structures.Removable physical structures are distinguished from sacrificialmaterials that burn out at elevated temperatures, and refer instead tosolid structures that are pulled out of the device.

FIG. 4 depicts in perspective view a green layer of anode material 24having a plurality of wires 92 extending all the way through andsurrounded by the anode material 24. The use of wires 92 to form spacedapart passages 14, 20 in the active area 50 is advantageous because theactive area 50 then has a solid support for the gas passages. The solidmaterial is first made as a paste, filled with anode, cathode or ceramicparticles, and then dispensed and dried around the wires 92 to fullysupport the wires. The solid material is necessarily porous for at leasta portion of the anode 24 and cathode 26. The wires 92 can be placed inparallel, if desired, and then the material is dispensed over the top ofthe wires. A vacuum can be pulled after dispensing the paste, in orderto remove any air pockets below the wires so that the wires 92 arecompletely surrounded. Alternatively, a layer of paste can be deposited,then the wires 92 positioned, and then more paste applied. Thus, a layercontaining the wires 92 may be formed separately, for example using amold and paste materials, and then dried to form a wire-containingpreformed sheet, which preformed sheets can then be stacked.Additionally or alternatively, the paste for one layer can be applied ontop of a preceding layer in a manner that embeds the wires 92 in thepaste of that layer, and that layer is then dried in place in the stack.Thus, the entire stack can be built sequentially on a surface in such away that each layer is built and dried, and then another layer is put ontop and dried, or each layer can be premade and treated as preforms, andthe stack built up from many different pre-made sub components, or anycombination of these two techniques can be used to assemble a completedevice stack.

Once the device stack is formed, it is laminated, and then the wires 92are removed. The layer-by-layer dimensions are better maintained duringlamination with the present invention because the green preform layersalready contain the wires 92 with the electrode material surrounding andconforming to the wire shape, such that the green layers need notconform around the wires 92 as the layers are pressed together. Theresult, for a single active cell 50, is shown in cross-section in FIG.5, after the wires 92 are pulled out, and after the porous anode andcathode materials are fired. Rather than a large flat passage 14adjacent the anode 24, as shown in FIG. 3, the device in FIG. 5 includesa plurality of small round fuel passages 14 embedded within the anode24, and the same is true for the cathode 26 and oxidizer passages 20.Round wires are not required, as other shapes can be used. Because thewires 92 are removed before baking the stack, binder removal from theporous materials and from any sacrificial layers will proceed morequickly because exit passages for the binder are already present. FIG. 6shows, for an anode 24, how the gas in operation of the device 10 canflow through the fine fuel passages 14, and then travel through theporous anode 24 to reach an electrolyte area 28. A single electrode canalso serve two electrolyte layers 28 on either side.

In the active cell 50, different combinations of materials can be usedin combination with the wires 92. FIG. 7 depicts, for an anode layer 24,a combination of a porous anode 24 a with the fuel passages 14 embeddedtherein and a non-porous anode 24 b adjacent thereto (and opposite theelectrolyte, not shown). FIG. 8 is similar to FIG. 7 but with the fuelpassages 14 formed along the interface between the porous anode 24 a andthe non-porous anode 24 b. With paste materials, a layer of the porousanode paste can be laid down first, followed by laying the wires 92 ontothe paste and pushing them halfway into the paste, and then applying thenon-porous anode paste over the wires. Depending on whether and how farthe wires are pushed into the porous layer will determine the positionof fuel passages at the interface, e.g., off-center and residing mostlyin the porous layer, off-center and residing mostly in the non-porouslayer, or centered halfway in each layer.

FIG. 9 shows how the paste materials can transition from one layer tothe next to give a grading in the thickness direction (z direction), forexample, a graded porosity with layer 24 a being highly porous, layer 24b having medium porosity, and layer 24 c having low porosity, forexample in a direction away from the electrolyte. While not shown,rather than a multi-layer anode 24 surrounding the wires 92, amulti-layer structure can include combinations of electrode and ceramiclayers, or a grading in which ceramic material is mixed with electrodematerial to transition from pure electrode to pure ceramic. Each layerin a multi-layer structure can be tailored to perform differentfunctions, such as one material being anode/cathode, and the other beingceramic or YSZ; porous versus non-porous; larger versus smaller pores;chemical composition variations; relative electrical conductivityvariations; relative ionic conductivity variations; variations in theability to bond to surrounding materials; or any other physical orchemical variation.

When coating the wires with the desired material to form a layer havingthe plurality of spaced-apart passages embedded therein, the materialcan completely cover or not completely cover the wires, and the properchoice of the coating conditions can help achieve the optimalperformance. Having a majority of the wire 92 surrounded by the materialof the layer achieves the objective of providing support for thestructure.

If the surrounding material does not exceed the top and bottom of thewires having a round shape, the intervening support material is a pillarshaped structure. This is the minimum structure necessary to give asolid support structure in the active area, such that it is not requiredthat the passages be completely encompassed within the electrode, onlymostly encompassed by virtue of being essentially sandwiched betweensupport structures. The support material can meet the wire exactly atthe top and bottom surfaces or the support material can be recessed onboth sides of the wires, either way forming a pillar structure.Additionally, an asymmetric structure can be formed where one side ofthe wires is exceeded and one side is not. By way of example, the pillarform, and in particular the recessed pillar form, can be created byusing a paste that becomes much thinner as the solvent dries out of thepolymer matrix or by shaving the top surface with a thin razor blade anddistorting down between the wires.

As opposed to varying the material composition in the thicknessdirection of the wires, FIG. 10 shows variation down the length of thewires 92 for an anode 24, in particular, an anode layer 24 a along afirst length portion, an anode layer 24 b along a second length portion,and an anode layer 24 c along a third length portion. Any number ofdifferent material types is possible. Variations of anodes, ceramics,and cathodes down the length of the wires 92 are also possible, suchthat the structure could contribute to the formation of a series fuelcell travelling down the length direction. Another variation is toreplace the anode layers 24 a and/or 24 c with sacrificial material toform sections having large volume flow paths in combination with thesupported flow sections, or to insert sacrificial segments that willform exit paths to the sides of the device 10.

With respect to the wires 92 or other physical structures, variationsare possible in terms of wire diameters, wire materials, and wireproperties. The wires can be 0.02 inch, 0.01 inch, 0.005 inch, or 0.002in, for example. The wires can be made of stainless steel, carbon steel,nickel, titanium, or any other appropriate material. The wires can bespring metal, annealed, flexible and have varying degrees of strength.The wires can be straight or curved, as discussed further below. Thewires can be round, oval, semi-circular, square, rectangular, or anyother shape, as desired. The plurality of wires in a single layer neednot all be of the same shape or dimension, and can be different in onelayer versus another layer. Additionally, the wires can change indimension and/or shape as they travel down the length of the device. Forexample, a wire can have a first diameter along the length of thepassive area of the device and gradually or sharply decrease to a seconddiameter in the active area of the device, for example, a smaller seconddiameter. In another example, the wire can have a first shape along thelength of the passive area of the device and gradually or sharply changeto a second shape in the active area of the device, such as a firstround shape and a second semi-circular shape or a second oval shape. Thechanges in diameter and shape may be designed to achieve objectives ingas flow properties and/or to achieve less resistance to the wires beingremoved after lamination. It may also be advantageous to heat the deviceafter lamination to facilitate the wire removal, for example, to about85° C., although other temperatures are contemplated. In one embodiment,the temperature of the device is raised to above the glass transitiontemperature (T_(g)) of the organic materials of the stick todramatically soften the material, allowing easy removal of the wires.Additionally, the wires may be coated, as necessary with a releaseagent. However, the use of heat may make the use of release agentsunnecessary. Wires may be used to form any combination of inputpassages, active passages, and exhaust passages. Further, within asingle layer, such as an anode layer 24, the wires 92 may be arranged inparallel in a single layer, or multiple spaced layers. The size of thewires, and thus the size of the formed passages, may also be varied inthe multiple spaced layer, for example, a row of smaller diameterpassages could be formed in anode layer 24 b of FIG. 7, and this rowcould be aligned or offset with respect to the passages in anode layer24 a, as desired.

Various methods are possible for connecting the gas supplies to the fueland air passages. In an elongated device, a fuel supply can be coupledto one end, and an air supply to the opposite end, for example, byplacing flexible supply tubes over the ends. In such embodiments, thefuel entering one end would have to exit the device at a point beforereaching the opposite end, since the opposite end is coupled to the airsupply. Thus, side exits or vertical exits have been contemplated inprevious designs. When using wires 92 to form the passages 14, 20 to andthrough the active area 50, the wires for forming the fuel passages, 14,for example, can extend lengthwise from a fuel input end of the deviceand terminate at the conclusion of the active area, or can proceed intothe opposite passive area but stop short of the opposite air input end.A side exit path can then be formed using sacrificial material oradditional wires in contact with the lengthwise wires, such as at theends of the wires, and extending widthwise to the side of the device.

Alternatively, the wires can extend through the entire length of thedevice, such that both the fuel and oxidizer passages 14, 20 extend froma first end 11 a to a second end 11 b, but then one of the set ofpassages 14 or 20 is sealed off at each end, such as by injecting asmall amount of ceramic or glass paste into the passages at the ends toplug them and seal them off, or by temporarily plugging the passages tobe kept with short wires and painting a paste of ceramic or glass overthe passages to be sealed, drying the paste, then removing the temporaryplugs. Exit passages to the sides or vertically would still need to beformed then ahead of the plugs. In yet another alternative, where thewires extend the full length of the device, supply of the gases may bemade by a plurality of supply tubes, for example, ceramic tubes, thatare sized to be inserted into the respective plurality of passages, intypical manifold fashion, but advantageously outside the furnace in thecold end region of the device.

In alternative embodiments, shown in FIGS. 11A-11B, 12A-12B, 13 and 14,curved wires can be used to form the passages 14, 20. In FIG. 11A, forforming the anode layer 24, the wires 92 are straight at end 11 a untilthey reach the end of the active area 50, then they curve toward oneside of the device 10 to form the fuel output 16 at the side. For thecathode layer 26, the wires 92 are straight from the opposite end 11 b,until they reach the end of the active area 50, then they curve towardone side of the device 10 to form the oxidizer output 16 at the side.With the anode layers 24 and cathode layers 26 stacked together, adevice 10 may be formed as shown. Supply tubes (partially depicted inphantom) can be fitted over each end 11 a, 11 b for supplying the fueland air, respectfully, to inlets 12 and 18, while the spent gases exitout the sides of the device 10 from outputs 16, 22 before reaching theends 11 a, 11 b.

In FIG. 11B, a two-layer electrode structure can be used to form thespaced-apart passive and active passages 14, 20 in one layer andspaced-apart exhaust passages 15, 21 in the other layer. In anode layer24 a, straight wires 92 are used from the end 11 a to the end of theactive area 50 to form fuel passage 14. A curved wire 92 is used inanode layer 24 b to form exhaust passages 15 from the active area 50 tothe side for the outlet 16 of spent fuel. The exhaust passages 15 (and21, not shown) need not extend through the entire active area 50, butcan begin within the active area 50, such as halfway into the activearea 50. As shown, the exhaust passages 15 are offset from the activepassages 14, but this is not required.

In FIGS. 12A-12B, showing an anode layer 24 in FIG. 12A and a resultingdevice 10 in FIG. 12B, the wires 92 curve the entire length of thedevice 10 from the input through the active area 50 and to the output,so as to form inputs 12, 18 and outputs 16, 22 in the sides of thedevice 10. While this may not be a preferred embodiment in terms ofconnecting the fuel and air supplies, manifold-type connections arenonetheless feasible.

To better provide for separate fuel and air connections, FIG. 13 usesthe same curved wires 92 as in FIG. 12A, but splits the ends 11 a, 11 bof the device 10 to form a pair of first end portions 11 a 1 and 11 a 2and a pair of second end portions 11 b 1 and 11 b 2. This constructionis made possible by the fact that the layers are assembled from thegreen state, and thus the green layers can be molded, cut and/or shapedto have the desired form. The pair of first end portions 11 a 1, 11 a 2can be coupled to fuel and air supplies to feed gases to the fuel andair inputs 12, 18, respectively, and the spent gases can exit fromoutputs 16, 22, respectively, in the pair of second end portions 11 b 1,11 b 2.

FIG. 14 depicts a combination of the various embodiments above,utilizing partially curved wires, straight wires, and a split end. Apair of first end portions 11 a 1 and 11 a 2 is formed to accommodateseparate fuel and air connections to inputs 12, 18, respectively, withonly first end portion 11 a 1 being curved. Wires 92 are used that curvefrom first end portion 11 a 1 into the active area 50 then straightenand exit at end 11 b. Straight wires 92 are used that enter at first endportion 11 a 2 and exit at end 11 b, such that both outputs 16 and 22are at the single end 11 b of the device.

FIG. 15 shows another embodiment for building a series fuel cellstructure in the vertical (thickness) direction. This can dramaticallyreduce the path length for the interconnect compared to other designsbecause the distance from one active cell to the next becomes very shortand very wide, and this gives the lowest resistance combination. Inaddition, the use of interconnect material, and possibly precious metal,is reduced overall.

FIG. 15 depicts in schematic cross-section two active cells 50 stackedin series, but many active cells 50 can be stacked one upon another bythis method. The anode layers 24 and cathode layers 26 are formed asdescribed above, for example, as shown in FIG. 6, and stacked withintervening electrolyte layers 28 to form a three-layer active cellstack 50 of anode 24/electrolyte 28/cathode 26. A non-conductiveinterconnect layer 50 a is positioned between each active cell stack 50,with each interconnect layer 50 a having a plurality of conductive vias52 extending there-through to make electrical contact with the cathode26 of one active cell 50 and the anode 24 of the next active cell 50. Tomake the interconnect layer 50 a, a green sheet of non-conductiveceramic material can be hole-punched to provide via holes 51, andconductive paste, for example, containing precious metal, can be filledinto the via holes 51 for making the electrical connection with theconductive vias 52.

The use of filled or plugged via holes can provide a potential source ofgas leaks, which negatively affect device performance, so an alternateembodiment is shown in exploded view in FIG. 16. As with FIG. 15, activecell stacks 50 are formed, but a variation is used to electricallyconnect the active cells 50 in series. In particular, the interconnectlayer 50 b is made of more than one ply (in this case two) where the viaholes 51 are offset. This offset technique can prevent or reduce theleakage of gas from one side to the other. Instead of a single sheet ofnon-conductive material, two non-conductive sheets are provided with viaholes 51, and a conductor layer 53 is printed on one side of each sheetand they are stacked with the printed sides facing each other, with thevia holes 51 offset so that they do not overlap. In this embodiment,there is no need to actually fill the via holes 51 with interconnectmaterial, as they can be filled instead with anode 24 or cathode 26material, as shown. This approach then saves on the use of preciousmetal. In the case of the cathode side, the material (LSM, for example)can be made dense so that it contributes to leak-prevention.

In the embodiments of FIGS. 15 and 16, the via holes 51 can be large orsmall, and can be plenty or few. By way of example, and not limitation,via holes 51 can be 0.1 inch (2.54 mm) in diameter, or can be 25 μm.

It was discussed above that the paste material deposited around thewires 92 can be varied in the length direction, for example, as shown inFIG. 10. This concept can be used to create a series design down thelength of the device 10, rather than vertically as shown in FIG. 15. InFIG. 17, a top view depicts an anode layer having alternating segmentsof ceramic support material 29 and anode material 24 embedding the wires92. A similar cathode layer may be formed with cathode material 26, andthese layers may be stacked with the segments of anodes 24 and cathodes26 aligned and with an intervening electrolyte layer 28 to form anactive cell layer having a successive series of active cells 50 down thelength, as shown in side view in FIG. 18. The series connections may bemade on the sides of the device 10 if all or a portion of the anodes 24and cathodes 26 extend the full width or at least to one side of thedevice 10, or internally using previously disclosed methods in priorapplications cited above, or methods disclosed herein.

One method for forming internal series connections is to include aninterconnect tab 54 for each electrode segment, as shown in FIG. 19(wires not shown). The exploded view depicts each of the anode layer(layer 1), a combination electrolyte 28/interconnect layer 50 acontaining both the electrolyte 28 and the conductive vias 52 (layer 2),and the cathode layer (layer 3), in top view and in alignment forstacking, and then in side view as stacked. The wires are not shown, butwould be extending through each of layers 1 and 3. The interconnect tab54 of the anode 24 of one active cell 50 is aligned with theinterconnect tab 54 of the cathode 26 of the next adjacent active cell50, and the conductive via 52 of interconnect layer 50 a is aligned withboth, thereby making the series connection between the adjacent activecells 50. Alternative interconnect tabs 54 are depicted schematically inFIGS. 20A and 20B, showing both a top view and a side view. In FIG. 20A,the tab is notched, which provides an interlock between the anodesegment 24, the ceramic support material 29 and the interconnect tab 54,which may contribute to leak prevention. In FIG. 20B, the interconnecttab 54 is a thin extension only at the surface that interfaces with theinterconnect layer 50 a, thereby minimizing the material used for theelectrical connection.

Referring to FIGS. 21A and 21B, in side view and top view, respectively,another series structure is depicted using alternating electrode andceramic support segments. In the stacking of the layers, the anodesegments in one layer are offset with respect to the cathode segments inthe other layer, with the combination electrolyte 28/interconnect layer50 a therebetween. The edge of the anode 24 of one active cell 50 isaligned with the edge of the cathode 24 of the next adjacent active cell50 to provide a small overlapping region, and the conductive vias 52 ofinterconnect layer 50 a are then aligned with that overlapping region.This design then eliminates the need for the interconnect tabs 54.Rather than the interconnect layer 50 a, the interconnect layer 50 b maybe used instead, which is formed from two sheets with the printedconductor layer 53 therebetween.

The various series designs enable any number of active cells, whethersituated in a single active layer sequentially down the length, orvertically by stacking active cells on top of each other, or acombination of both. Thus, small devices or large devices can beprovided with relatively high voltage. For example, a handheldelectronic device could be provided with the design of FIGS. 21A-21B togive low wattage with a high voltage, for example, 0.25 W and 3.6 V.

While the present invention has been illustrated by the description ofone or more embodiments thereof, and while the embodiments have beendescribed in considerable detail, they are not intended to restrict orin any way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. The invention in its broader aspects is thereforenot limited to the specific details, representative apparatus and methodand illustrative examples shown and described. Accordingly, departuresmay be made from such details without departing from the scope of thegeneral inventive concept.

What is claimed is:
 1. A method of making a monolithic fuel cell device,comprising: dispensing a paste of anode material around a firstplurality of spaced-apart removable physical structures such that thepaste flows at least partially around each of the first plurality ofspaced-apart removable physical structures; drying the paste with thefirst plurality of spaced-apart removable physical structures embeddedtherein to form an anode layer; dispensing a paste of cathode materialaround a second plurality of spaced-apart removable physical structuressuch that the paste flows at least partially around each of the secondplurality of spaced-apart removable physical structures; drying thepaste with the second plurality of spaced-apart removable physicalstructures embedded therein to form a cathode layer; positioning anelectrolyte layer between the cathode layer and the anode layer to forma stack, removing the first and second plurality of removable physicalstructures from the stack to form spaced-apart passages in each of theanode layer and the cathode layer; and sintering the stack, wherein anactive cell of the stack is formed by the anode layer in opposingrelation to the cathode layer with the electrolyte layer therebetweenwith spaced-apart passages defined in sintered anode material andsintered cathode material.
 2. The method of claim 1, further comprisingdispensing a paste of ceramic material around the first and secondplurality of spaced-apart removable physical structures adjacent to theanode materials while in the mold and the cathode materials while in themold to at least partially surround each of the first and secondplurality of spaced-apart removable physical structures with the ceramicmaterial, wherein during drying, the ceramic paste forms a passivesupport adjacent each of the anode material and the cathode material,and wherein sintering forms a passive support structure having passagesformed therein that transitions integrally to the spaced-apart passageswithin the active cell.
 3. The method of claim 1 wherein dispensing oneor both of the pastes includes dispensing a layer of paste into the moldand wherein the method further includes placing the first and/or secondplurality of spaced-apart removable physical structures on the layer ofpaste and then further dispensing the paste over the first and/or secondplurality of spaced-apart removable physical structures.
 4. The methodof claim 1 wherein dispensing the pastes further includes dispensing atleast two different material sub-layers to form a first sub-layer ofporous anode material or a first sub-layer of porous cathode pastematerial and a second sub-layer of non-porous anode material or a secondsub-layer of non-porous cathode paste material dispensed over the firstsub-layer.
 5. The method of claim 4 wherein the first sub-layer isdispensed around the respective first or second plurality ofspaced-apart removable physical structures such that, after sintering,the spaced-apart passages are embedded in and supported by the sinteredporous anode or the sintered porous cathode.
 6. The method of claim 4wherein the first sub-layer is dispensed around one side of therespective first or second plurality of spaced-apart removable physicalstructures and the second sub-layer is dispensed around the opposingside of the respective first or second plurality of spaced-apartremovable physical structures such that, after sintering, thespaced-apart passages are supported by the sintered porous anode or thesintered porous cathode on one side and supported by the sinterednon-porous anode or the sintered non-porous cathode on the opposingside.
 7. The method of claim 4 wherein the at least two differentmaterial sub-layers include a plurality of sub-layers each with adiffering porosity, with the anode layer and/or the cathode layerdecreasing in porosity in a thickness direction away from theelectrolyte layer.
 8. The method of claim 1 wherein dispensing thepastes to form one or both of the anode layer and cathode layer includesdispensing the paste with a varying composition in the thicknessdirection of the removable physical structures, wherein the variation incomposition is selected from amount of porosity, size of pores, chemicalcomposition, relative electrical conductivity, relative ionicconductivity, bonding properties, ratio of anode or cathode material toceramic material, or a combination thereof.
 9. The method of claim 8wherein the varying composition includes a graded porosity with theporosity decreasing in a thickness direction away from the electrolytelayer.
 10. The method of claim 1 wherein dispensing the paste includesdispensing the paste of the anode material and dispensing the paste ofthe cathode material with a varying composition in the length directionof the removable physical structures.
 11. The method of claim 10 whereinthe varying composition includes alternating dispensing of the paste ofthe anode material or the paste of the cathode material according to apredetermined length portions with dispensing of a paste of a ceramicmaterial.
 12. The method of claim 1 wherein in the stack an active cellportion is formed by the anode layer in opposing relation to the cathodelayer, the method further comprising: placing a ceramic support layerover the active cell portion and providing an exposed conductive portionextending through the ceramic support layer; and repeating dispensingthe paste of the anode material and the paste of the cathode materialand positioning the electrolyte layer therebetween to form additionalactive cell portions with the anode layer of one active cell portionadjacent the cathode layer of the next vertically adjacent active cellportion, with the ceramic support layer between the vertically adjacentactive cell portions with the exposed conductive portion electricallyconnecting the active cell portions in series.
 13. The method of claim12 wherein the ceramic support layer is a green sheet of non-conductiveceramic material with spaced apart holes that are filled with conductivepaste to form the exposed conductive portion and during placing theceramic support layer, the green sheet is positioned on the active cellportion.
 14. The method of claim 12 wherein the exposed conductiveportions are formed by providing two ceramic support layers havingspaced via holes formed therein and coating one side of each of the twoceramic support layers with a conductive material and placing the coatedsides in contact with each other with the via holes of one ceramicsupport layer offset from the via holes of the other ceramic supportlayer.
 15. The method of claim 1 wherein the removable physicalstructures change shape along the length of thereof.
 16. The method ofclaim 1 wherein removing the first and second plurality of removablephysical structures includes heating the respective layer.
 17. Themethod of claim 1 wherein dispensing the paste of the anode materialand/or the dispensing of the paste of the cathode material includesdispensing the paste in a mold.
 18. The method of claim 1 whereindispensing the paste of the anode material or dispensing the paste ofthe cathode material includes dispensing the paste onto the electrolytelayer.